1. Field of the Invention
This invention relates to increasing the apparent temporal or spatial resolution of a video image which is displayed on a raster or matrix display element, without a required increase in the number of video image elements in the acquisition of the image.
2. Description of the Prior Art
As television and related image technology develops, there is increasing emphasis on improving the quality of displayed images in order that they appear more real and pleasing to the human observer. Two of the parameters which affect image quality, and therefore are subject to improvement, are spatial and temporal resolution. Spatial resolution, simply put, is the number of elements or pixels which are used to make up an image, and correspondingly, temporal resolution is the number of pixels per unit time which make up a moving image. Desirable qualities of a display system, such as broadcast television or computer graphics, will include having as many pixels per image, or frame, and as many pixels or frames per unit time as is economically feasible. Unfortunately, increasing the number of pixels per frame or the number of frames per second is a costly improvement, therefore many schemes have been developed to improve the resolution of the displayed image, while reducing the number of pixels used.
One scheme which is utilized to improve the cost to performance ratio, and is finding widespread use in consumer television receivers, involves increasing the apparent resolution of the displayed television image by replicating scan lines. The present standard U.S. television system is fixed by law and standardization to a scanning system having 525 lines, of which approximately 48 are utilized for the actual picture display. With the development of large CRT and projection displays, these 480 scan lines are often quite visible, and it is desirable to reduce this visibility. Many manufacturers effectively double the number of scanning lines displayed by repeating each scanning field of the image. This double scanning process is performed with the air of a large memory which stores the previously received scan or field, allowing in effect both the present and the previous field to be displayed line by line. One such system which accomplishes this type of improvement, is known as up scan conversion, and was used by Siemens Corp. in the 1988 time frame. Another use of scan conversion is described by Naimpally et. al. in "Integrated Digital IDTV Receiver With Features" published in IEEE Transactions on Consumer Electronics, vol. 34, No. 3, Aug. 1988. These and other scan conversion techniques provide a much more pleasing image to the viewer, even though, as one skilled in the art will recognize, the number of distinct displayed pixels is not increased. What gives rise to the perceived improvement in the image is that by displaying each scan line twice, thus filling in the void between scanning lines, a much more pleasing image results. One of the major disadvantages of these systems is the cost of the memory system which is utilized to store the previous image frame. The memory system cost can be a substantial percentage of the cost of a consumer television display. Another disadvantage is that the apparent horizontal and diagonal resolution are not increased. A diagonal line, for example, will still have a coarse stair stepped shape due to the scanning lines of the raster, even though the number of scanning lines is increased.
Other improvement systems, such as various Improved Definition Television Systems (IDTV), Advanced Television Systems (ATV), and High Definition Television Systems (HDTV) operate to increase the resolution and other quality related aspects of television systems. Many of these systems resort to various techniques for such quality improvements, some of which generate unwanted artifacts.